Schedule I Financial Statements of Parent Company Statements of Income (Details) - USD ($) $ in Millions	3 Months Ended								7 Months Ended	10 Months Ended	12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
OPERATING EXPENSES:
Operating and maintenance											$ 1,163.0	$ 1,218.5	$ 1,115.8
Total Operating Expenses											3,769.5	3,962.0	3,342.3
INCOME FROM OPERATIONS	$ 153.0	$ 521.7	$ 271.7	$ 197.5	$ 165.8	$ 538.7	$ 271.7	$ 209.6			1,143.9	1,185.8	933.6
OTHER INCOME (EXPENSE):
Equity in earnings from subsidiaries											8.3	9.8	5.4
Other expense											(78.2)	(76.9)	(78.7)
Total Other Expense, Net											(36.1)	(39.0)	(54.4)
Interest expense											383.9	374.0	279.6
INCOME BEFORE INCOME TAXES											723.9	772.8	599.6
Income tax expense (benefit)											102.2	97.0	59.0
Net income attributable to Evergy, Inc.	51.0	364.5	133.4	69.4	63.9	366.8	139.7	99.5			618.3	669.9	535.8
COMPREHENSIVE INCOME
NET INCOME	$ 54.0	$ 367.5	$ 136.3	$ 72.2	$ 66.7	$ 370.9	$ 144.6	$ 103.4			630.0	685.6	546.0
Derivative hedging activity
Loss on derivative hedging instruments										$ (69.8)	0.0	(64.4)	(5.4)
Income tax benefit											0.0	16.5	1.4
Net loss on derivative hedging instruments											0.0	(47.9)	(4.0)
Reclassification to expenses, net of taxes											(3.0)	(1.5)	0.0
Derivative hedging activity, net of tax											3.0	(46.4)	(4.0)
Total other comprehensive income (loss)											0.6	(47.0)	(3.0)
COMPREHENSIVE INCOME											618.9	622.9	$ 532.8
Parent
OPERATING EXPENSES:
Operating and maintenance									$ 54.6		39.3	19.4
Total Operating Expenses									54.6		39.3	19.4
INCOME FROM OPERATIONS									(54.6)		(39.3)	(19.4)
OTHER INCOME (EXPENSE):
Equity in earnings from subsidiaries									364.7		683.4	698.2
Investment earnings									26.3		32.1	32.7
Other expense									(2.6)		(0.1)	(0.1)
Total Other Expense, Net									388.4		715.4	730.8
Interest expense									19.6		86.3	60.7
INCOME BEFORE INCOME TAXES									314.2		589.8	650.7
Income tax expense (benefit)									(10.7)		(22.7)	(13.7)
Net income attributable to Evergy, Inc.									324.9		612.5	664.4
Derivative hedging activity
Loss on derivative hedging instruments									(5.4)		0.0	(64.4)
Income tax benefit									1.4		0.0	16.5
Net loss on derivative hedging instruments									(4.0)		0.0	(47.9)
Reclassification to expenses, net of taxes									0.0		3.0	1.5
Derivative hedging activity, net of tax									(4.0)		3.0	(46.4)
Other comprehensive income (loss) from subsidiaries, net									1.0		(2.4)	(0.6)
Total other comprehensive income (loss)									(3.0)		0.6	(47.0)
COMPREHENSIVE INCOME									$ 321.9		$ 613.1	$ 617.4